So I'm painting with the brush tool, and I mess up and hit "E" on my keyboard for the eraser but the tool doesn't change. I hit "cmd+/-" and nothing happens, I hit "M" for marqee nothing happens.
When I click my mouse in the gray area thats part of the window plane like layers/tools etc, I am able to use my keyboard shortcuts again.
Its as though photoshop didn't recognize that I had stopped using the brush tool and kept me locked in until I clicked on something that is not part of the canvas to "wake it up".
I have no idea why this is happening.
I had that "issue" too, even though it's not an issue.
The explanation is that due to your shortcut combo, you end up pressing Alt key which takes focus to the upper menu tab ( file, edit and so on, you can see them selected ). You need to place focus on you drawing board again by either clicking on it or pressing Alt again.
This loss of focus also happens when using Alt+Tab to change between windows.
You'll get used to it.